High-risk critically ill patients often require mechanical ventilation either to primarily support the respiratory function or when the ventilation is insufficient to maintain adequate gas exchanges as a result of other organ impairment. In order to tolerate this aggressive mechanical support, enhance patient synchrony with the ventilator, and relieve pain and anxiety, analgesia and sedation are provided. It is suggested that an inappropriate use of sedation and analgesia may prolong the duration of mechanical ventilation and increase the risk of specific adverse outcomes such as ventilator associated pneumonia. Despite the widespread use of sedation, little information is available concerning the effect of varying the level of sedation on patients' subsequent mental health. We designed a randomized controlled trial to investigate the efficacy of sedation with the goal of maintaining the patient cooperative and interactive compared to the administration of sedation with the goal of maintaining the patient sedated. The first goal will be achieved by a discontinuous injection of a sedative, while the second goal will be achieved by a continuous infusion of the same sedative. In both groups pain relief will be provided in the same fashion with equal endpoints on a pain scoring scale. Our primary aim is to investigate whether differences in the occurrence of post-traumatic stress disorders (PTSD), anxiety, and depression are related to the choice of sedation-analgesia strategies. Secondary endpoints include the length of ICU stay, as indicated by the time to discharge from the ICU, the time to separation from mechanical ventilation, the rates of pulmonary and extra-pulmonary complications, and hospital length of stay. These endpoints will be compared between the two groups.